The present invention relates generally to insulators. More specifically, the present invention relates to a funnel-shaped support insulator for a high voltage conductor retained in a tubular housing.
An insulator of this type is known, for example, from Swiss Patent Specification No. 547,024. The insulator described there has a uniform wall thickness and is anchored by its outer edge in a recess of a grounded metal housing part. On both sides of the outer edge of the insulator there are annular grooves which are open inwards in the housing part and which act as a particle trap because of the reduced electrical field prevailing there. However, in the case of an insulator mounted and designed in this way, voltage increases and harmful glow discharges associated with these cannot be prevented, especially at the groove edges adjacent to the insulator.
One primary object of the invention is, therefore, to develop the insulator of the type in question in such a way that it is possible to obtain a retention of the insulator on the grounded housing part which retention is free of inadmissible field increases and which can be carried out by simple means.
This object and others are achieved by providing the funnel-shaped support insulator with a wall thickness which decreases from an inner edge of the insulator towards its outer edge and in which a plurality of lobes engaging the housing are located on the outer edge of the insulator. The insulator according to the invention is characterized in that there are in its outer regions, adjacent to grounded housing parts, electrical field gradients which are specific and can therefore be monitored easily, so that harmful phenomena, such as glow discharges, are virtually eliminated.
If the insulator according to the invention has the lobes projecting beyond the outer edge of the insulator in both an axial and a radial direction, then the electrical field-strength distribution at the outer edge of the insulator can be monitored particularly well, since the outer edge of the insulator has on all sides an exactly specific distance from the grounded housing. As a result, voltage increases and consequently glow discharges between the grounded housing and the insulator can be prevented in an especially simple way.
If the insulator according to the invention has the lobes cast in one piece with the insulator, then this insulator can, furthermore, be produced in an especially simple and economical way. At the same time good preconditions are provided for arranging the insulator largely free of stress in the housing.
A further embodiment of the insulator has a corrugated surface facing the conductor with depressions being provided in the corrugated surface. There is as little solid insulation as possible in the region of the lobes making the engagement with the grounded housing, thereby ensuring an additional improvement of the field-strength conditions in the outer edge regions of the insulator according to the invention.
If the insulator according to the invention has the depressions made as recesses, and parts of the edge of the insulator are removed, then its dielectric properites are also additionally improved because of the supplementary reduction of solid insulation in the edge regions.